Multi-select and RF channel usage

[ocguard]

I'm not sure if the answer to this question is P25 protocol-wide, manufacturer-dependent, programming-dependent, or (most likely) some combination of the three.

Assuming a single-site or a single-cell P25 simulcast, when a dispatcher at a control station uses a multi-select function to simultaneously transmit on multiple talk groups, does the system use a single voice RF channel to complete this call? Or a voice RF channel for each talk group selected?

I was considering proposing the option of staffed stations within our EMS system each being assigned a talk group dedicated ONLY to the dispatcher broadcasting a call to that station, allowing a radio assigned to that talk group to be used as basically a selective call dispatch medium. The caveat is, if multiple stations are dispatched simultaneously, would this max out the voice channel capacity on the system or cell. Now that I've seen the P25 dispatch pager concept, this seems even more enticing of an option.

Please feel free to chime in with any pertinent brand of system you may have the answer for. Thanks!

 

[WA0CBW]

In the Motorola consoles it is possible to do it both ways. Obviously using an RF channel for each talk group multi-selected can use up the RF resources very quickly. The console should be able to re-group each talk group to a single group for multi-select functions. Check out the features of your console for the multi-select functions.
BB

 

[riveter]

Typically, one RF channel is used for an MSEL. The system just directs all member talkgroups to that RF channel to listen to the traffic on the MSEL every time one of them is activated.

 

[ocguard]

Typically, one RF channel is used for an MSEL. The system just directs all member talkgroups to that RF channel to listen to the traffic on the MSEL every time one of them is activated.

This was a SmartNet (the system and the operator shall remain nameless), but I remember one time experimenting by multi-selecting most of the console and hitting the crash bar (our name for the CCM transmit)... there were 16 immediate talk permit tones followed by about 40 sequential ones as the console cycled through each call grant. Field users got system busy for 19 seconds. We got a memo shortly after. That was old status bit technology, though. We did learn that if we wanted to make a large simul-select call and only use one RF channel, we could do a quick console patch and instant transmit. Good old days.

 

[mostinterestingman]

"If the tallest building in your county is a grain silo, you DON'T need 800mhz!"

I absolutely love this ^^

 

[riveter]

These days it's all IP based. The call is assigned the same group call IP for all of the talkgroups in the MSEL, so it should just come out of the radio net interface as one RF channel.